TY - JOUR A1 - Poyraz, Ö. A1 - Schmidt, H. A1 - Seidel, K. A1 - Delißen, Friedmar A1 - Ader, C. A1 - Tenenboim, H. A1 - Goosmann, C. A1 - Laube, B. A1 - Thünemann, Andreas A1 - Zychlinsky, A. A1 - Baldus, M. A1 - Lange, A. A1 - Griesinger, C. A1 - Kolbe, M. T1 - Protein refolding is required for assembly of the type three secretion needle JF - Nature structural & molecular biology N2 - Pathogenic Gram-negative bacteria use a type three secretion system (TTSS) to deliver virulence factors into host cells. Although the order in which proteins incorporate into the growing TTSS is well described, the underlying assembly mechanisms are still unclear. Here we show that the TTSS needle protomer refolds spontaneously to extend the needle from the distal end. We developed a functional mutant of the needle protomer from Shigella flexneri and Salmonella typhimurium to study its assembly in vitro. We show that the protomer partially refolds from α-helix into β-strand conformation to form the TTSS needle. Reconstitution experiments show that needle growth does not require ATP. Thus, like the structurally related flagellar systems, the needle elongates by subunit polymerization at the distal end but requires protomer refolding. Our studies provide a starting point to understand the molecular assembly mechanisms and the structure of the TTSS at atomic level. PY - 2010 DO - https://doi.org/10.1038/nsmb.1822 SN - 1545-9993 SN - 1545-9985 VL - 17 SP - 788 EP - 792 PB - Nature Publ. Comp. CY - New York, NY, USA AN - OPUS4-21726 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Seidel, R. A1 - Kraffert, K. A1 - Kabelitz, Anke A1 - Pohl, M.N. A1 - Kraehnert, R. A1 - Emmerling, Franziska A1 - Winter, B. T1 - Detection of the electronic structure of iron-(III)-oxo oligomers forming in aqueous solutions JF - Physical Chemistry Chemical Physics N2 - The nature of the small iron-oxo oligomers in iron-(III) aqueous solutions has a determining effect on the chemical processes that govern the formation of nanoparticles in aqueous phase. Here we report on a liquid-Jet photoelectron-spectroscopy experiment for the investigation of the electronic structure of the occurring iron-oxo oligomers in FeCl3 aqueous solutions. The only iron species in the as-prepared 0.75 M solution are Fe3+ monomers. Addition of NaOH initiates Fe3+ hydrolysis which is followed by the formation of iron-oxo oligomers. At small enough NaOH concentrations, corresponding to approximately [OH]/[Fe] = 0.2–0.25 ratio, the iron oligomers can be stabilized for several hours without engaging in further aggregation. Here, we apply a combination of non-resonant as well as iron 2p and Oxygen 1s resonant photoelectron spectroscopy from a liquid microjet to detect the electronic structure of the occurring species. Specifically, the oxygen 1s partial electron yield X-ray absorption (PEY-XA) spectra are found to exhibit a peak well below the onset of liquid water and OH (aq) absorption. The iron 2p absorption gives rise to signal centered between the main absorption bands typical for aqueous Fe3+. Absorption bands in both PEY-XA spectra are found to correlate with an enhanced photoelectron Peak near 20 eV binding energy, which demonstrates the sensitivity of resonant photoelectron (RPE) spectroscopy to mixing between iron and ligand orbitals. These various signals from the iron-oxo oligomers exhibit Maximum intensity at [OH]/[Fe] = 0.25 ratio. For the same ratio, we observe changes in the pH as well as in complementary Raman spectra, which can be assigned to the Transition from monomeric to oligomeric species. At approximately [OH]/[Fe] = 0.3 we begin to observe particles larger than 1 nm in radius, detected by small-angle X-ray scattering. KW - Iron-oxo oligomers KW - XPS KW - Electronic structure PY - 2017 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-433468 DO - https://doi.org/10.1039/c7cp06945f SN - 1463-9076 SN - 1463-9084 VL - 19 IS - 48 SP - 32226 EP - 32234 AN - OPUS4-43346 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gao, S. A1 - Hou, J. A1 - Deng, Z. A1 - Wang, T. A1 - Beyer, Sebastian A1 - de Oliveira Guilherme Buzanich, Ana A1 - Richardson, J. J. A1 - Rawal, A. A1 - Seidel, R. A1 - Zulkifli, M. Y. A1 - Li, W. A1 - Bennett, T. D. A1 - Cheetham, A. K. A1 - Liang, K. T1 - Improving the Acidic Stability of Zeolitic Imidazolate Frameworks by Biofunctional Molecules JF - CHEM N2 - Zeolitic imidazolate frameworks (ZIFs) have been widely investigated for their use in separation, gas adsorption, catalysis, and biotechnology. Their practical applications, however, can be hampered by their structural instability in humid acidic conditions. Here, guided by density functional theory calculations, we demonstrate that the acidic stability of two polymorphic ZIFs (i.e., ZIF-8 and ZIF-L) can be enhanced by the incorporation of functional groups on polypeptides or DNA. A range of complementary synchrotron investigations into the local chemical structure and bonding environment suggest that the enhanced acidic stability arises from the newly established coordinative interactions between the Zn centers and the inserted carboxylate (for polypeptides) or phosphate (for DNA) groups, both of which have lower pKas than the imidazolate ligand. With functional biomolecular homologs (i.e., enzymes), we demonstrate a symbiotic stability reinforcement effect, i.e., the encapsulated biomolecules stabilize the ZIF matrix while the ZIF exoskeleton protects the enzyme from denaturation. KW - Zeolitic Imidazolate Frameworks KW - Biofunctional Molecules KW - X-ray Absorption Spectroscopy PY - 2019 DO - https://doi.org/10.1016/j.chempr.2019.03.025 VL - 5 IS - 6 SP - 1597 EP - 1608 PB - Elsevier Inc. AN - OPUS4-48702 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Sadowski, A. A1 - Seidel, M. A1 - Al-Lawati, H. A1 - Azizi, E. A1 - Balscheit, Hagen A1 - Böhm, M. A1 - Chen, Lei A1 - van Dijk, I. A1 - Doerich-Stavridis, C. A1 - Kunle Fajuyitan, O. A1 - Filippidis, A. A1 - Winther Fischer, A. A1 - Fischer, C. A1 - Gerasimidis, S. A1 - Karampour, H. A1 - Kathirkamanathan, L. A1 - Subramanian, S. A1 - Topkaya, Cem A1 - Wagner, H. N. R. A1 - Wang, J. A1 - Wang, J. A1 - Kumar Yadav, K. A1 - Yun, X. A1 - Zhang, P. T1 - 8-MW wind turbine tower computational shell buckling benchmark - Part 1: An international ‘round-robin’ exercise JF - Engineering failure analysis N2 - An assessment of the elastic-plastic buckling limit state for multi-strake wind turbine support towers poses a particular challenge for the modern finite element analyst, who must competently navigate numerous modelling choices related to the tug-of-war between meshing and computational cost, the use of solvers that are robust to highly nonlinear behaviour, the potential for multiple near-simultaneously critical failure locations, the complex issue of imperfection sensitivity and finally the interpretation of the data into a safe and economic design. This paper reports on an international ‘round-robin’ exercise conducted in 2022 aiming to take stock of the computational shell buckling expertise around the world which attracted 29 submissions. Participants were asked to perform analyses of increasing complexity on a standardised benchmark of an 8-MW multi-strake steel wind turbine support tower segment, from a linear elastic stress analysis to a linear bifurcation analysis to a geometrically and materially nonlinear buckling analysis with imperfections. The results are a showcase of the significant shell buckling expertise now available in both industry and academia. This paper is the first of a pair. The second paper presents a detailed reference solution to the benchmark, including an illustration of the Eurocode-compliant calibration of two important imperfection forms. KW - Wind turbine tower KW - Computational KW - Shell buckling KW - Benchmark PY - 2023 DO - https://doi.org/10.1016/j.engfailanal.2023.107124 SN - 1350-6307 VL - 148 SP - 1 EP - 23 PB - Elsevier Science CY - Oxford AN - OPUS4-57019 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -